Warm season vegetables are sensitive to frost. There are many types of vegetables that can grown successfully within a high tunnel. Many growers have used high tunnels for early tomatoes. However, other choices include peppers, squash, eggplant, and snap or pole beans.

2. What are some examples of cropping patterns for a high tunnel?
At least two crops per year can be produced using a high tunnel. For example, in Missouri, tomatoes can be planted as early as March within a high tunnel, and harvest can begin in-June. Depending on the variety and type of tomato chosen, harvest can continue through July. At this point, the tomatoes can be removed, the soil fertilized and tilled, and a second crop of tomatoes, peppers or cucumbers can be established for fall harvest. In late November, a cool season vegetable can be planted and over-wintered in the high tunnel for early spring harvest.

3. How are tomatoes grown within a high tunnel?

Single layer rowcovers cover staked tomatoes

Tomatoes are grown on raised beds with organic or plastic mulch. The raised bed ( 6”) will facilitate drainage and keep the root system warmer. Plastic mulch (black, clear, or IRT) will also increase soil temperatures. Drip irrigation is applied to water and fertilize the tomatoes through the growing season. Row covers, a lightweight fabric, must be used to provide early frost protection. The tomatoes can be either staked or caged.

4. How many tomato plants can I plant in a 20’ x 96’ high tunnel?
The optimal spacing for tomatoes in a high tunnel is 6 square feet per plant. Therefore, approximately 300 plants can be planted per house.

5. Is pollination of tomatoes adversely affected by the high tunnel?
No. Tomatoes are self-pollinated. In research at the University of Missouri, we have not experienced pollination problems with tomatoes in a high tunnel. Air movement, which reduces humidity and vibrates the flower, is important for good pollination. If you have to keep the vents closed for an extended period of time, you may want to shake the cages or stakes to facilitate pollination. If you are using rowcovers, you should remove them when your plants are flowering and the sidewalls are rolled-up. If temperatures are projected to get 55F or less, the rowcovers should remain on the plants.

6. What is an average yield for high tunnel tomatoes?
In Missouri, we average approximately 10 lbs. of tomatoes per plant over a 4 week harvest period (mid June to mid July). Percentage of unmarketable fruit is much less relative to field tomatoes.

7. Do I need to spray tomatoes within a high tunnel for disease and insect control?
High tunnels provide a protected environment for crop growth. However, this does not mean you will not have any harmful diseases or insects. Protecting the crop from rain will significantly reduce disease problems. However, you should scout your crop for any sign of disease. In Missouri, the insects we have encountered on tomatoes include aphids (Myzus persicae), hornworms (Protoparce quinquemaculata), and fruitworms (Helicoverpa zea). Many of these insects can be controlled by biological methods (beneficial insects) or using biological insecticides (Bt insecticides).

8. Are certain tomato cultivars best suited for high tunnel production?

Any field or garden tomato will perform well within a high tunnel. If the objective is to produce early tomatoes, the best choice would be a hybrid, determinate cultivar that concentrates its fruit-set within a narrow window (4-6 weeks). Indeterminate types will perform well within a high tunnel, however, these types of tomatoes continue to set fruit through the summer and fall. Indeterminate tomatoes would be well-suited for late summer and fall tomatoes.

9. Are tomatoes daylight sensitive?
We have two questions in one: 1) How much light do tomatoes need? and 2) Does the duration of light (day) affect tomato fruit set?

How much light do tomatoes need? Generally speaking, for winter production of tomatoes, light intensity of about 3500 foot candles is adequate. When light is not sufficiently intense, a disorder known as blotchy ripening occurs.mThis also can occur in field production when there is an extended period of cloudy weather. Greenhouse growers can increase light intensity by using white mulch as the floor of the greenhouse to reflect light back into the crop canopy and by being sure the film covering the greenhouse or high tunnel is clean and relatively new. The ability of polyethylene film to transmit light is reduced as the film ages, even before the aging is visible to the human eye. So don’t wait until it gets yellow or so old it cracks before replacing it. Tomatoes also respond to the wavelength of the light with blue and red light increasing vegetative growth and red and far-red light increasing flowering. Light is essential for photosynthesis with creates the carbohydrates necessary for plant growth. Poor light intensity=poor growth, poor fruit set, poor fruit development, and poor flavor. Tomatoes respond best to maximum sunlight. Cultivars bred for greenhouse production are bred to produce high quality fruit when grown in lower light conditions (and higher humidity) than those bred for field production. They are best adapted for late fall and early spring production.

Tomatoes are daylength neutral, which means that tomatoes flower the same regardless of how many hours of darkness or light they receive. However, this does not mean that the best tomatoes are grown under continuous light. Tomatoes require an extended dark period for best quality because it is during the dark period that the products of photosynthesis are transported to the developing fruit, providing sweetness, flavor, and color.